Particle size and surface effects on critical thickness for ferroelectricity of BaTiO3 by ab initio calculations

The particle size and surface effects of the critical thickness for ferroelectricity of nanoscale BaTiO3 particles is investigated using a first-principles molecular orbital (MO) method and population analysis for net charge and overlap population. A series of models composed of a Ba8Ti7O6 cluster and point charges surrounding the cluster are employed for the calculations of the electronic structures of the BaTiO3 particles, with the size of the model defined by the size of the point charge array. The calculation results show that the critical thickness for the ferroelectric-to-paraelectric transition of nanoscale BaTiO3 particles decreases with decreasing basal area of the rectangular particles. We conclude that in the ferroelectric phase of BaTiO3 particles, ferroelectricity still exists extremely close to the surface.